217 



vex, nearly circular ; sides and front margin uniformly rounded ; posterior 

 margin very obtusely angulated at the beak, on each side of which, a por- 

 tion of the cardinal edge equal to one-fourth of the whole width of the 

 shell, is nearly straight ; umbo very small ; beak apparently depressed to 

 the hinge line and not projecting beyond it ; cardinal angles compressed, 

 broadly rounded ; a wide shallow mesial sinus extends from the front mar- 

 gin about half way to the beak ; elsewhere the valve is gently convex, or 

 nearly flat. 



Ventral valve acutely conical, with a flat triangular area which is per- 

 pendicular to the plane of the lateral margin, its base half the width of the 

 whole shell. In the apex of this valve there is a minute circular aperture, 

 and in one specimen a dark line extends from it down the middle of the 

 area, which appears to represent the foraminal groove of this genus ; but 

 in two other specimens of the ventral valve, with the area well preserved, 

 there is no indication of a groove. Surface with very fine concentric striae. 



Width of dorsal valve, about 1 line ; length, about f of a line. The 

 height of the ventral valve is about 1 line. 



The form of this species is very like that of A. subconica (Kutorga), 

 but that species is twice the size of this, and has the area distinctly 

 grooved. 



Locality and Formation. P, four miles north-east from Portland Creek, 

 Newfoundland ; Quebec group. 



Collector. J. Richardson. 



ORTHIS DELICATULA. (N. sp.) 



Description. Shell thin and flat, semi-elliptical, hinge line straight, 

 equal to about twice the length of the shell : sides and front uniformly 

 rounded. Ventral valve with a narrow mesial elevation in the upper half, 

 elsewhere flat ; beak and umbo slightly elevated above the hinge line ; 

 area narrow or linear. The dorsal valve is almost flat with a shallow 

 mesial groove. Surface with very fine radiating striae, about ten in the 

 width of one line. Width of an average specimen, 4 lines ; length 2 

 lines. 



Locality and Formation. N, Table Head and Pistolet Bay ; P, four 

 miles north-east of Portland Creek, Newfoundland ; Quebec group. 

 Collector. J. Richardson. 



OTHER SPECIES OF ORTHIS. 



1. ORTHIS ELECTRA, ante, p. 79, occurs at Table Head, Port aux 

 Choix, and Point Rich in Divisions H and I. At Table Head some of 



